1. Field of the Invention
The present invention relates to optical systems used in digital projection systems and more particularly to a compact anamorphic lens having two components which widens the image by a factor of 1.3 to 2.0.
2. The Prior Art
In digital projection, liquid crystal devices (LCDS) and digital mirror devices (DMDs) which have an aspect ratio of 4 to 3 or 5 to 4 are normally used. Consequently, projection with non-anamorphic lens produces images with the same aspect ratio as these devices. These projection formats, however, do not correspond to the best psychological visual perception of the human being. In order to more closely approximate this visual perception, it is desirable to widen the horizontal dimension of the images. Such widening can be accomplished with anamorphic lens. Anamorphic optical systems, also called anamorphotes, differ from traditional lens primarily in that the focal length in the horizontal direction markedly deviates from the focal length in the vertical direction. The ratio of these two focal lengths is called the anamorphic factor.
In U.S. Pat. No. 5,930,050, a lens of this kind is described. This lens exhibits an excellent state of correction. This result was achieved by a five-lens element afocal supplementary lens, the partial refractive powers of which, compared with other anamorphotes available on the market, were significantly relaxed. This arrangement, however, as the professional knows, leads to an enlargement of the height and of the diameters of the anamorphic lens, which in turn greatly increases the cost of its manufacture.
In accordance with the invention, a compact, anamorphic lens with high efficiency is produced at a reasonable cost. The lens has a first afocal component B1 in front of the projection lens which in turn has two subcomponents U1 and U2. Each subcomponent has high refractive power in the horizontal direction. The lens also has a second component B2 placed behind the projection lens, which has very little refractive power in the vertical direction. The anamorphic lens widens the image by a factor of 1.3 to 2.0.